1. Field of the invention
The present invention pertains to pipe welding apparatus. More specifically, the present invention pertains to internal clamps for aligning pipe sections in end-to-end relationship for welding. In particular, the present invention pertains to internal line-up clamps suitable for welding pipe in cross-country pipe lines.
2. Description of the Prior Art
Pipe lines, of course, have been used for many years to transfer fluid products from one point to another. Many of these pipe lines are several hundred miles long. This is especially true of pipe lines which transport hydrocarbon products, gas, oil, gasoline, etc. Typically, such pipe lines are formed of pipe sections which are welded end-to-end as they are installed along a pipe line right-of-way. Such cross-country pipe lines may vary in diameter from eight inches to sixty inches and even more.
In welding one pipe section to another, it is important that the adjacent ends of the pipe sections being welded be coaxially aligned and that the pipe be as near to a true circle as possible. For this reason, internal pipe clamps have been developed for aligning and holding contiguous pipe sections while they are being welded together. A typical internal pipe line-up clamp of the prior art is shown in U.S. Pat. No. 3,044,431. Such line-up clamps typically include a frame assembly which support a pair of axially spaced and radially expandable clamp assemblies. The frame assembly usually carries some source of fluid pressure, typically a pressurized air tank, which provides the force necessary for operating various components of the clamp. Some type of drive apparatus is usually supported by the frame assembly for propelling the clamp apparatus through sections of pipe as the pipe is joined together by welding. Controls for operation of the line-up clamp are typically placed at the front of the clamp where they may be reached for manual operation. In some cases, e.g. after welding is finished at a joint between two pipe sections, the controls are not within reach. For these situations, a mechanism is provided which may include a long handle or reach rod which extends to and slightly beyond the forward end of the last pipe section so that the controls may be manipulated by an individual standing at the forward end of the last pipe section. Most, if not all, of the currently used pipe line-up clamps operate in this fashion. Other such examples of the prior art may be seen in U.S. Pat. Nos. 3,425,614 and 4,140,262. While these designs vary somewhat, particularly in the design of the clamping assemblies, they operate in the same general manner.
An internal pipe line-up clamp of the prior art typically operates in the following manner. After welding of a pipe joint, the clamp assemblies are retracted by manipulating the long reach rod which slightly extends from the end of the last pipe joint. Then the drive mechanism is actuated, using the reach rod, causing the line-up clamp to be propelled forwardly through the last pipe joint. As this occurs, the operator must be careful to place the distal or free end of the reach rod within the next pipe section to be welded to the pipe line. Initially, however, enough space must be provided between the end of the last welded pipe section and the next one to be welded thereto so that the operators may control the operation of the internal pipe line-up clamp being propelled toward them.
Typically, the line-up clamp of the prior art is also provided with a pair of cables which extend forward of the line-up clamp for a distance considerably shorter than the reach rod which extends through the next pipe joint. One of these cables is attached to a control device which deactivates the drive motor and the other is attached to a braking device or a motor reversing device. As the line-up clamp approaches the end of the last welded pipe section, these two cables exit the end of the pipe section where they must be grabbed by a worker. Usually one worker grabs the drive cable, deactivating the drive motor, and another worker grabs the brake or reverse motor drive cable, activating the brake assembly (or reversing the drive motor) to arrest the forward movement of the line-up clamp. The length of the control cables are designed so that skilled workers may stop the line-up clamp just short of being ejected from the pipe section. The workers then, by manipulation of accessible controls, position the line-up clamp forwardly or rearwardly so that the rearmost clamp assembly is properly positioned just inside the last welded pipe section. Then the rearmost clamp assembly is expanded for clamping engagement with the interior walls of the last welded pipe section.
After movement of the line-up clamp has been arrested and the rearmost clamp assembly expanded, the next pipe section to be welded to the pipe line is slid over the forward end of the line-up clamp and aligned end-to-end with the last welded pipe section until the two pipe sections are properly spaced for the welding together thereof. At this time, the forwardmost clamp assembly is positioned internally of the next pipe section to be welded to the pipe line. Then by manipulating the reach rod which extends from the front of the line-up clamp through the pipe section to be welded, the forwardmost clamp assembly is actuated expanding into clamping engagement with the interior walls of the pipe section to be welded. With expansion of both clamp assemblies, the ends of the two pipe sections to be joined are coaxially aligned and the walls are forced into true circular alignment. The welding of the pipe sections then proceeds. After the welding joint is completed, both clamp assemblies are retracted by manipulation of the reach rod, the drive mechanism is activated and the cycle repeated for another section of pipe.
These internal pipe line-up clamps are quite heavy, some of the larger sizes typically weighing four to five thousand pounds. In addition, they may be propelled through the pipe line at speeds approaching six feet per second and if on a downwardly inclined grade move even faster. From the previously described typical operation of pipe line-up clamps of the prior art, it can be easily understood that the workers who work with such clamps are subjected to possible injury or even death if the movement of the clamp is not arrested in time to prevent it being driven from the end of the last welded pipe section. Even though a worker is not injured by the line-up clamp itself, the long reach rod which extends through the next pipe section to be welded and the control cables associated with the drive mechanism and the brakes are potentially hazardous.
Even if a worker is not injured when movement of the line-up clamp fails to be arrested in time, there are other problems associated with ejection of the line-up clamp from the end of the last welded pipe section. Such ejection may cause damage to the line-up clamp requiring repair or replacement thereof. In addition, the clamp must be lifted and placed back in the pipe section from which it was ejected. Since these line-up clamps are extremely heavy, some as much as several thousand pounds, heavy lifting equipment and considerable time are required. Loss of time may seriously affect the profits of a pipe line contractor, many of whom bid their jobs on the basis of completing a weld every three or four minutes.
In an attempt to overcome some of the deficiencies of line-up clamps of the prior art, particularly the possibility of the line-up clamp being ejected from the end of the last welded pipe section, additional protections have been sought. For example, U.S. Pat. No. 3,462,059 discloses a line-up clamp which is provided with a lever which pivots downwardly as the line-up clamp begins to exit the end of the pipe. As it pivots, the speed of the device which propels the line-up clamp through the pipe is reduced. After a little further movement another lever exits the pipe and pivots downwardly shifting the drive mechanism to a reverse position and with the aid of a stop mechanism is supposed to align the clamp for expansion of the rear clamping assembly. While the purpose of these mechanisms is to solve the aforementioned problems, it is doubtful this has been accomplished since this type of line-up clamp is not generally known and has not apparently met with commercial success. This may be due to the fact that with the speeds and momentum involved in pipe line-up clamps, the operation and control of this prior art design may not have been fast enough.
Pipe line-up clamps of the prior art, including those presently used, have been effective for many years in welding pipe sections. However, they are potentially hazardous in operation and in some cases may result in lost time. Thus, improvements in the operation, safety and efficiency of such pipe line-up clamps are much needed and sought.